Using a conventional solid-state reaction, followed by sintering at 1080°C-1200°C Li 2 (Zn 1Àx A x )Ti 3 O 8 (A = Mg, Co and x = 0.02 -0.1) ceramic system with >96% density were prepared. The XRD patterns of the sintered samples revealed single-phase formation with a cubic crystal symmetry. The molecular volume shows good linear relationship with x value. The microwave dielectric properties of Li 2 (Zn 1Àx A x )Ti 3 O 8 ceramics exhibited a significant dependence on the x value and to some extent on the morphology of the specimens. The Li 2 (Zn 0.94 Mg 0.06 )Ti 3 O 8 ceramics possess e r = 26.1, Q 3 f = 150 000 GHz, and τ f = À13.9 ppm/°C, and Li 2 (Zn 0.92 Co 0.08 )Ti 3 O 8 ceramics show e r = 24.7, Q 3 f = 140 000 GHz, and τ f = À13.4 ppm/°C, respectively. It indicates a substantial increase in the Q 3 f in comparison with that of pure Li 2 ZnTi 3 O 8 . The microwave dielectric properties of these partially substituted ceramics are reported for the first time.

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In this work, undoped Mg 2 TiO 4 thin films were fabricated on p-type Si(111) substrates by the sol-gel method, and the red photoluminescence (PL) of the films is introduced and discussed. According to the experimental results, the red emission appears when the films have been thermally treated at higher temperatures, which have a long range and well-organized crystalline arrangement. Furthermore, to have better realization of the red emission mechanism of Mg 2 TiO 4 films, the optical band gap of Mg 2 TiO 4 (E g Mg2TiO4 ) was estimated at 3.7 eV; furthermore, 325 nm (corresponding energy, hm = 3.82 eV > E g Mg2TiO4 ) and 633 nm (corresponding energy, hm = 1.96 eV < E g Mg2TiO4 ) excited light sources were used to clarify the position of the defect levels. In addition, the influence of annealing atmospheres (O 2 , air, and vacuum) on the red emission of our samples is also discussed. A significant variety of red emissions can be found between these annealing conditions: the red emission can be effectively enhanced by O 2 annealing, but weakened by vacuum annealing. Results reveal that the red emission of Mg 2 TiO 4 thin films may be highly dependent on the completeness of the O-X-O (X = Mg, Ti) bonds.

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